As is widely known, submarine telecommunication systems use cable in order to supply power to the equipment used along a transmission line where the transmission is usually performed on optical fibers. A fairly substantial longitude of these cables is laid down in deep sea. Repeaters or regenerators are used to receive line currents and in turn supply voltage to be fed to optical fibers carrying telecommunication traffic signals. The submarine cables can be damaged by external causes giving rise to power fault in the system as a whole or in a part thereof. The power fault causes in turn loss of traffic on the optical fibers associated to the faulty power feed. When the damage is located in deep sea, the task of repair become substantially difficult and costly. Nevertheless it is usually desired that the traffic is restored as soon as possible.
In normal operation, the supply voltage of a long submarine system can be up to 18 kV. The voltage is supplied by two power supply units, one at each end of the system.
The individual voltage rating of these power supplies is often not adequate to supply the full system voltage on their own, therefore the system powering is shared between the various power supply units, at least between two of them. Typical power supplies may only be capable of supplying 12 kV of the 18 kV maximum required. Therefore, in the event of a power supply failure or a cable shunt fault currently the system will not be able to carry traffic because of the shortage of supply current due to the reduced power supply voltage capability.
FIG. 1 shows the voltage requirements of a typical submarine system in terms of system voltage as a function of system length and number of fiber pairs. In this figure various graphs 1, 2, 3, 4, 5 and 6 are shown, each of these graphs correspond to the voltage requirements when the number of fiber pairs use is 1, 2, 3, 4, 5 and 6 respectively. As can be seen in this figure, on long systems, for example with a length of 8000 km, with many fiber pairs, for example six, the voltage requirements can be as high as about 18 kV. On the other hand it can also be observed in the figure that as the number of fiber pairs is reduced, the voltage requirements for the system are reduced as well. For example, it is readily appreciated that by using two fiber pairs, the voltage requirements of the system can be reduced to about 12 kV for the same distance of 8000 km.
Also as already mentioned above, if a fault occurs such as a power supply failure or a shunt fault in the cable, then a single 12 kV power supply is not capable of powering the complete system giving rise to the loss of the traffic in the whole system.
It is therefore desired to provide an efficient solution for a fast and efficient restoring of the traffic when such power faults occur.